The overall goal of this project is to advance effective and efficient remediation strategies for subsurface systems contaminated by dense non-aqueous phase liquids (DNAPLs), which are among the most common and most challenging of Superfund contaminants. The specific aims involve the evolution of fundamental scientific understanding and application of a promising class of dense-brine remediation technologies developed by the project leader's research group. The specific aims include the following: (1) to extend this class of technologies to new sets of hydrological and contaminant source conditions that are both common and challenging;(2) to evaluate the impact of remediation on exposure;and (3) to formulate, solve, and use improved models of these systems to help advance our understanding and application of these technologies. A combination of laboratory and modeling approaches will be used in this work. A wide range of experiments will be performed, from batch experiments to determine detailed phase behavior and physicochemical characteristics to experiments in heterogeneous three-dimensional flow cells intended to mimic the natural systems of concern. Mathematical modeling will be essential for advancing and testing our fundamental understanding, designing experiments and interpreting the results, predicting the effect of likely field conditions that cannot be evaluated directly in the laboratory, and advancing potentially more efficient strategies to be evaluated in the laboratory or field. This work is of significance because it deals with a mainstream issue of importance to Superfund?remediation of contaminated subsurface systems, addresses especially difficult and prevalent classes of contaminants, considers realistic systems, and will advance fundamental understanding. Outcomes that directly impact Superfund sites are expected, including field-scale use of the technologies developed in this project.